Updated: Aug 2, 2021
A conversation with Mary Putman. By Nia Brown
Mary Putman is an astronomy professor and researcher at Columbia, as well as the Director of Undergraduate Studies for Astronomy and Astrophysics. For her outstanding work on the formation and evolution of galaxies (like our own and otherwise) and star formation among other concepts, she has been awarded a Hubble Postdoctoral Fellowship and a National Science Foundation CAREER award.
B&W: You once described your research to me as looking at what fuels galaxies and galaxies that eat other galaxies, do you want to explain more?
MP: Yes, so what I look at is how galaxies get more fuel to form stars. So a star like our Sun is a second generation star so it formed from when our Milky Way galaxy brought in more fuel, it was able to form our Sun and this process is ongoing. Our galaxy forms about a Sun per year, maybe a little bit more but the equivalent of a Sun a year. The way it does that is by bringing in more hydrogen gas, which is the main fuel for star formation. So I look at how that process happens and it happens both from streams of gas that come in from the intergalactic medium as well as what you are remembering, our galaxy will eat smaller galaxies. We can map that process using telescopes that can see little galaxies being shredded by bigger galaxies.
B&W: Yeah, and I saw you worked with GALFA, the program mapping neutral hydrogen. You want to explain why hydrogen is so interesting here?
MP: Yeah it is a big survey, it uses the Arecibo radio telescope in Puerto Rico, it was the largest single dish telescope but now the one in China is open so technically that one is bigger now. So why hydrogen—it is the most abundant element in the universe. It was formed in the Big Bang and everything heavier than helium and a little lithium and beryllium was actually formed later in stars, so hydrogen was there from the beginning. It is still the most common by far throughout the universe in terms of the elements. Because it is so abundant, there is an atomic transition that hydrogen makes naturally that we can detect with our telescopes. It emits a very distinct wavelength of light.
B&W: So a lot of your research seems to be concerning the beginnings of the universe and you received a Hubble Postdoctoral Fellowship which is for outstanding research broadly relating to NASA Cosmic Origins Program’s goals, so why is this question of where humans and the cosmos came from so interesting for you?
MP: You know the idea of humans not knowing about their environment is a little [strange]—I mean why would you not want to know? I think it is natural human curiosity that you want to know something about your environment and that goes everywhere from New York City to our Universe as a whole. Just trying to understand what is going on up there, there are so many open questions and all we get in astronomy is the light to interpret, you get to apply direct physics but you also get a certain aspect of creativity in terms of explaining and coming up with ideas of what is going on.
B&W: When explaining science to people, I feel like it always comes back to that, trying to explain where we come from—very broadly throughout all sciences.
MP: Yeah that is the other aspect, what is the origin of Earth, of humans, but each thing builds on the next. To have Earth, you need to have our star the Sun, to have our star the Sun, you needed to have the Milky Way galaxy, to have the Milky Way galaxy, you had to form the universe and have structure formed in the universe. You need each of those steps to really understand our origins.
B&W: So your research, galaxies eating other galaxies, that is a metaphor and in popular science and science writing in general I think we rely on metaphors a lot. A lot of the time, different groups, different writers end up reusing the same metaphors, do you think that could potentially limit people’s understanding of the concepts—always using the same metaphors?
MP: That is an interesting question. You are correct in particular when they try to publicize science, they’ll use metaphors that are very limited. A classic metaphor that is used that is very limited is trying to understand the expansion of the universe using things like the surface of the balloon—dots on the surface of the balloon that get further away as the balloon expands being celestial objects. That is only two dimensions when in reality, the universe is four dimensions—at least. So you are always going to be somewhat limited by making analogies. In terms of alternatives, I am not sure, because we need to be able to speak a language that everyone can relate to—which is an ongoing problem in the sciences. We have a lot of jargon and we’ve went through at least eight years, usually more like ten years, of schooling to learn all the physics and the astronomy. So it is always going to be a challenge. More visuals are great, I think people are picking up on more interactive visuals that can help.
B&W: Your research uses a lot of simulations, does that seem to help when explaining things to people? I know that is how a lot of research astronomy is done in general.
MP: I think so, the movies take a lot of explaining as well, it is a real art to figure out how to do those well so that people from a wide variety of backgrounds can look at them and see what is going on. I think if anything it helps just because people are drawn to that—it is moving, it has color. Also, the simulations are key throughout astronomy, just in terms of interpreting our data. The data gets so complex, in particular because I work with gas, which has so many hydrodynamical effects that can happen. The simulations help a lot.
B&W: I think a lot of the times, and I once worked for an online popsci start-up publication, what gets “clicks” in writing about astronomy are stories like “this signal might be from aliens” though all of those recent incidents have been just from man-made electromagnetic sources so it is just interesting when people share those articles but don’t know about something like LIGO which is way more important and newsworthy in the field of astronomy. It has been called revolutionary actually.
MP: Yeah it is amazing they have actually detected gravitational waves. Well, I guess an alien has more of a potential direct impact whereas something like gravitational waves are a little bit like “oh is that going to affect me? No, not at all, ok, next” whereas an alien could potentially fly into your neighborhood or something, I don’t know maybe that is why.
B&W: Yeah, the theatrics and excitement of it.
MP: I mean we can always try to stretch things to link to those kind of natural interests of people, no matter what. Like this formed because this formed and what not.
B&W: Well, going back to LIGO, it has been considered as adding another dimension to our understanding of astronomy, that we can detect and potentially measure gravitational waves, past light and other electromagnetic sources. How do you see that expanding and what could be the next dimension of being able to measure and understand space?
MP: Gosh, I feel like that’s something that if I knew the answer to, I’d get a Nobel Prize. I’m pretty sure the people that proposed gravitational waves are getting a Nobel Prize. Of course the gravitational waves are exciting, though with that we are a little bit limited in which objects we can study yet. That doesn’t diminish how exciting they are, though there is a limited set of people that can study those, in relation to their objects, right now.
B&W: Yeah so what kind of access do the researchers have to apparatus here at Columbia and what is the protocol for different teams at different institutions using each other’s telescopes and equipment?
MP: Well that is a very big question, we could be here a while. Well, in terms of what Columbia has access to, it is a little odd compared to its peers in that it doesn’t have access to more [equipment]. This is something we are working on, to get involved either with one of these large surveys coming up and in particular access to a larger telescope, so [we’ll have to] propose to [observatories] to observe our objects. There are two telescopes down in Arizona that we are a part of. The model for getting involved in these kinds of things has changed over time just because the costs have gone up so high. Now that we are going to 30 meter optical or the millimeter ray down in Chile with so many dishes—it is billions of dollars. Now with some of the big optical telescopes, they’ve tried to get different university consortiums together. Funding from the government keeps getting narrower and narrower.
B&W: I think earlier this year, President Obama tried to propose around 18 billion more dollars funding for NASA and that seemed spurred by, looking at a lot the rhetoric, Charles Bolden reaffirming it is a primary goal of NASA at this point to improve the Orion manned-spacecraft program and try to go to Mars. But that no doubt has been affecting what the National Science Foundation can give out, too, right?
MP: So that is how I do a lot of my research, I get these three year NSF grants from the government, that is how I pay my graduate students and collect my data.
B&W: Do you have something to say about why going to Mars is so important? I know this is not really related to your research but I ask that question a lot, I don’t think I necessarily see that much exciting or practical gain of a man going to Mars but I think that has been particularly emphasized recently, in movies as well as in current discussions and programs.
MP: Well if it was a woman, then it would be exciting. I wouldn’t be too excited about a man going to Mars.
B&W: Ha, well I suppose I was just referencing the movie.
MP: No, don’t worry, you are totally right. The human part of it is mainly for inspiration. It was the same thing with the moon, you can get a lot more done by sending these rovers. And given the cost benefit, sending rovers will get you further. But the whole exploration aspect, I think you can’t beat that. For me, it does sound very exciting if someone is actually willing to [go to Mars] and someone is willing to pay for it. I’m not sure I am excited enough to say that the government should spend that much money on it. I like the idea of these private organizations getting in the game and doing that. [Government funding for Mars exploration] unfortunately would affect a lot of our funding, because it is not necessarily separate from what goes to NASA. That could pull a lot of money away from a lot of other things being researched. I am a little nervous about that. Otherwise it is exciting and would do a lot in terms of people’s interest, kind of like what you said about aliens. A human going to Mars—the whole field would get a big push from that.
B&W: What new programs or topics in astronomy lately have been really exciting to hear about?
MP: Well obviously the gravitational waves are great. The other is the planet stuff is always exciting—it is still a relatively new field. We can find another Earth-like planet or that we are now trying to detect atmospheres on the planets and different things like that. JWST, which is the next space telescope after the Hubble Space Telescope, is called the James Webb Space Telescope and it focuses in the infrared wavelengths which will do a lot in terms of understanding how planets form and planets themselves. In my area, there’s been an instrument on the Hubble in the ultraviolet [wavelengths] that has shown us that around a galaxy, you look with your eyes and you can see stars and what you think of as a galaxy, but actually about ten times further out, the galaxy extends. All this stuff that surrounds a galaxy is not detectable by most telescopes but it is detectable by this ultraviolet spectrograph. So that’s been very interesting, the gas way, way out far from where you normally think a galaxy ends.
B&W: Most of, or entirely, what you look at, is so far away and it does depend on our own capabilities and instruments what we see and what we miss. Can we tell what an atmosphere [on an exoplanet] is from the radiation and color it gives off?
MP: Yeah you look for spectral lines, the different elements, the different energy levels between the electrons jump around—there is a distinct signature for the elements and molecules. We are pushing the limits for that in terms of planets right now.
B&W: Speaking of the limits of what we can see and understand, your research, involves dark matter, you want to explain, to start with, the current understanding of what it is?
MP: Anyone who works on galaxies has to think about dark matter on some level just because it is the dominant component of the galaxy, it is probably 90% of the mass of a galaxy. For what I do, it dictates the motions of the gas because how something moves relative to something else is dependent on how massive the two bodies are. If you add a lot of mass from this dark matter, then stuff is going to move faster. The current thinking is that dark matter is cold, which means it is a relatively massive particle and that is doesn’t move super fast. With that cold, dark matter, the way structure forms in the universe, is you start with small things and build up to larger things. So that also has implications on my research, it predicts there should be lots of these small, dwarf galaxies, the building blocks of larger galaxies and we haven’t found a lot of those yet. With galaxies, most people tend to focus on more massive galaxies and what they do, not the little dwarfs.
B&W: Massive things tend to give off more energy, so they are just more easily detectable I imagine.
MP: Yeah, exactly, that is one reason why they have been the focus before, you see them more readily. The dwarfs are harder to find.
B&W: And it may be more exciting to write about grand things like “supermassive black hole does this” or “super giant star collides with this other huge object.” Are a good number of astronomy papers open source?
MP: All of them, well not all of them, almost all, we were one of the first fields to develop this kind of [open] archive, it is called Astro-ph that everyone puts their papers on now and it is all open source. [Papers] are published in journals that cost money but as soon as it is accepted, and sometimes even as soon as it is submitted, it goes into this other archive. So that is what most of us look at every morning, the Astro-ph listing for the day.
B&W: Do you think making the bulk of the knowledge open so early, ahead of other fields, is because astronomy is very collaborative and in some cases simply being on different parts of the world can help with certain projects?
MP: Yeah maybe, I actually don’t know, that is an interesting thing to look into more why astronomy was so ahead of the game there.
B&W: For apparatus and labs you directly deal with, what is it like, it is more virtual now right? Over correspondence and the computer?
MP: So when I was a graduate student, I would go to a telescope once a month when I was doing a large survey and we had to go and get the data but now they have moved to a model where they have telescope operators collecting most of the data for telescopes. So it can be somewhat rare now that graduate students, or I, go to the telescopes. Now we put in the proposal and if we get the time, [data] is taken by the telescope operator and sent to us on the computer and we analyze it on there.
B&W: Is that less fun, maybe?
MP: Yeah, I think you miss something not going to the actual instrument in terms of the experience and learning. Though obviously it saves time. I think you might get better data overall, there is trained people taking it, otherwise often you make some mistakes initially, right, because you have never used that [equipment]. Those kind of mistakes are exactly why the operators are doing this right now because some of these facilities have gotten so expensive, they just don’t want to mess around with an astronomer learning how to do it.
B&W: Are there sci-fi, movies, representations that you really like or don’t like for various reasons?
MP: In general I like sci-fi a lot, a good sci-fi is always a movie I’ll choose to go to. Or a book, I am reading one now, a Larry Niven book. Bad sci-fi—I actually think it is funny. Something like Deep Impact, you roll your eyes but it is kind of funny too, you almost enjoy it in another way. I guess the ones I don’t enjoy are the ones that get too violent, which today is most of them.
B&W: Yeah a lot of people worry about an asteroid, I guess not a lot of people but I see that more often than it is warranted I think.
MP: That’s a thing in astronomy that would affect you now potentially. But yeah I don’t think it’s likely it would happen too soon.
B&W: The NASA Near Earth Object program, that is monitoring things that are around us and in various sized orbits around us, we can reasonably know that there is nothing about to hit us.
MP: We have a pretty good handle on what is going on out there with the big ones, so I think we are pretty safe.
B&W: Maybe one more question, people like Carl Sagan, Neil deGrasse Tyson, underrated, overrated, or rated just the right amount?
MP: Ha, oh, that is an interesting question, I guess that depends on who is rating them. Those types of people are amazing in terms of what they are able to do for science and getting it out in the community. I mean they do get tremendously big heads and they could be a little arrogant. But I don’t know, it is ok. I don’t have to deal with them personally so I’m not that worried. I’m just really impressed with being able to communicate science to the public like that.